The field of medical imaging includes many well-known techniques for subdermal imaging of tissues and structures beneath the skin of a patient in a non-invasive manner. These imaging techniques commonly emit a form of electromagnetic energy that penetrates one or more tissue layers of the patient. Common examples of existing medical imaging techniques include X-Rays, positron emission tomography (PET) scans, and ultrasounds. A more recently developed medical imaging technique transmits microwave energy into a patient's body. This technique detects structures within the patient's body by detecting the reflections or backscatter occurring when the microwaves encounter a structure that reflects the microwave energy.
Subdermal imaging has many possible medical applications, and one application of immediate importance is the detection of growths and tumors in breast tissue. Breast cancer is a serious disease that kills tens of thousands of women every year in the United States alone. The use of X-Ray mammography has helped to detect breast tumors earlier, allowing early treatment that greatly improves the survival rate. However, X-Rays are high-energy ionizing radiation known to promote the development of cancers in human tissue. Thus, there is an undesirable tradeoff between not testing breast tissue for cancer and risking an undetected cancerous growth, or testing more often and increasing the risk that the testing technique itself will cause cancer to develop. Other imaging techniques that avoid the use of ionizing radiation such as an ultrasound may be much less effective at detecting tumors in the breast tissue.
Microwave imaging techniques present many advantages over other imaging techniques for detecting cancerous tumors, especially tumors in breast tissue. Unlike the energy used in an X-Ray, microwave energy is non-ionizing when penetrating human tissue. The non-ionizing radiation does not pose the cancer risk of the ionizing X-Ray radiation. Further, tumors in breast tissue are known to have a significant and consistent contrast to the microwaves in comparison to surrounding healthy breast tissue. The significant contrast characteristic means that a microwave that passes through healthy breast tissue also reflects off the surface of a tumor. By detecting the backscatter pattern of the reflected microwave energy, the tumor can be detected and imaged non-invasively.
While microwave imaging techniques have many advantages, the structure of the human body presents difficulties in using microwave imaging devices to effectively identify and image tumors. One such problem is that the human body has many layers of heterogeneous tissues, with the skin being the outermost layer. As stated above, microwave energy passes through the healthy breast tissue and reflects off the surface of cancerous growths. However, the microwaves also tend to reflect off the surface of human skin, which is often referred to as the “skin reflection.” The skin reflection causes noise in the reflected microwave signals, potentially obscuring reflections that may come from a tumor inside the patient's body from reflections are merely from the patient's skin. A system for microwave imaging that reduces noise introduced by the skin reflection benefits the fields of biomedical imaging and oncology.